Heretofore, a dry development system has widely been used for an electrostatic latent image developing method such as in electrophotographic copying machines from viewpoint of safety and reliability.
In addition, as a method for fixing a toner image transferred to a paper medium after being developed by the dry development method, a heat roll fixing system has been widely used from viewpoints of handling ease of the apparatus and high productivity. Recently, in order to realize power consumption conservation and shortening of warming-up time, methods in which a thin endless film layer having a specific heat as the fixing roll, are employed.
Recently, together with advanced development of copying machine technology, copying machines with high productivity and high reliability have been developed. In order to pursue high productivity and high reliability, not only enhancement of mechanical performances of a copying machine but also high performance toner, is essential.
As an approach to realize high productivity, high-speed fixing ability of toner at low temperature have been attempted. As a means for attaining high-speed fixing ability of toner at low temperature, technologies to lower fusion viscosity of a binder resin, i.e., to use a composition having a binder resin whose glass transition temperature is low or to lower the molecular weight of the binder resin, are cited.
However, the above-mentioned means noticeably reduce internal coagulation force of toner when it is in a fusing state, markedly narrowing the fixing temperature allowance. Accordingly, undesirable offset often occurs. In addition, the above-mentioned means also reduces internal coagulation force of toner when it is in a solid state. Therefore, when an automatic double-sided copy mode (ADU mode) is used, contamination of copied images due to contact between the paper feeding roller and paper or rubbing by other sheets, called "smearing" is caused. In addition, when the above-mentioned means are used, movement property of molecule chains of the binder resin is increased when the temperature is high. Accordingly, toners easily coagulate and fuse each other so that they are not suitable for practical use. In the above-mentioned manner, high speed and low temperature fixing of toner is accompanied by various problems. Therefore, in order to obtain toner suitable for practical use, it is necessary to balance the above-mentioned performances and problems.
In the past, there was one approach to control toner's visco-elasticity and thereby to obtain toner having favorable high speed and low temperature fixing performance was made.
For example, Japanese Patent Publication Open to Public Inspection (hereinafter, referred to as Japanese Patent O.P.I. Publication) No. 21557/1986 discloses the use of a developer whose main components are a binder resin and a colorant. The main component of aforesaid binder resin is composed of a vinyl-containing polymer, wherein one cm.sup.3 of aforesaid binder resin is extruded from a nozzle whose diameter is 1 mm and the length is 1 mm under the constant temperature climbing rate of 6.degree. C./min. and a load of 20 kg/cm.sup.2 by the use of a high bridge-type flow tester so that the degree of flowing out is measured and that, when the natural logarithm of the apparent viscosity calculated from aforesaid value is plotted against temperature, the absolute value of the inclination of the graph is 0.15 Ln (the apparent viscosity in terms of poise)/.degree. C. or less.
Japanese Patent O.P.I. Publication No. 101961/1988 discloses a toner component, containing a vinyl polymer, wherein the number average molecular weight is 1,000-10,000, the weight average molecular weight/the number average molecular weight is 41-200, its glass transition temperature is 50.degree.-70.degree. C., viscosity at 110.degree. C. is 5,000-5,000,000 poise in terms of shear rate of 1 sec.sup.-1 and viscosity is 10-1,000 poise at 190.degree. C. in terms of shear rate of 1 sec.sup.-1 as the major component.
Japanese Patent O.P.I. Publication No. 133065/1989 discloses a toner, containing a binder resin and a colorant, containing fusion viscosity is 5.times.10.sup.5 -10.sup.6 poise at 110.degree. C. and that is 9.times.10.sup.4 -3.times.10.sup.5 poise at 120.degree. C.
Japanese Patent O.P.I. Publication No. 122659/1991 discloses a toner for heating and fixing whose major binder resin is a resin wherein the flowing starting temperature (Tfb) by means of a high-bridged-type flow tester is 75.degree.-105.degree. C., the absolute value of the inclination of a graph at Tfb +20 when the common logarithm log.eta.' of fusion viscosity (.eta. ) is plotted on the temperature is 12 log (fusion viscosity in terms of poise)/.degree. C. or more, the absolute value of the inclination of a graph at Tfb+40.degree. C. is 4.4 log (fusion viscosity in terms of poise) and the constant logarithm of the fusion viscosity at Tfb+40.degree. C. is 4.4 log (fusion viscosity in terms of poise).
Japanese Patent O.P.I. Publication No. 303447/2989 discloses a toner for electrostatic latent developing, containing a styrene resin, as a major component, wherein the molecular weight distribution is at least in the range of 1.times.10.sup.4 or less and 5.times.10.sup.5 or more, the storage modulus is 1.times.10.sup.3 dyn/cm.sup.2 or more and the loss modulus is not more than 5.times.10.sup.3 dyn/cm.sup.2.
Japanese Patent O.P.I. Publication No. 67154/1992 discloses a toner, composed of a binder resin and a colorant, wherein the weight average molecular weight of the binder resin is 50,000-5,000,000 and when toner is 100.degree.-150.degree. C. the temperature difference necessary to change toner viscosity due to heating from 5.times.10.sup.6 -5.times.10.sup.4 poise is 32.degree. C. or more.
Japanese Patent O.P.I. Publication No- 338972/1992 discloses a toner whose major component is a binder resin and a colorant wherein the binder resin is composed of (a) 70-80 parts by weight of a styrene copolymer A wherein GPC molecular weight peak Lp is 5.times.10.sup.3 -1.5.times.10.sup.4 and (b) 30-20 parts by weight of a styrene copolymer B wherein GPC peak Hp is 4.times.10.sup.5 -2.times.10.sup.6, styrene monomer content Wl (weight %) in L.sub.p and styrene monomer content Wh in H.sub.p are respectively 50 weight % or more and concurrently with this Wl and Wh form a mixed resin wherein Wl&lt;Wh, when aforesaid resin has the storage modulus of 5.times.10.sup.3 to 5.times.10.sup.4 l at 170.degree. C. provided that the angular frequency .omega. of 10 rad/sec the dynamic loss tangent (tan 8) is 1.2 to 3.5 and the dynamic viscosity ratio is in the range of 500.ltoreq..eta.'.ltoreq.500 (poise).
Japanese Patent O.P.I. Publication No. 353866/1992 discloses a toner for electrophotography having a rheological property of, under measurement distortion of 1 deg. when the measurement frequency is 1 Hz, (1) the falling starting temperature of the storage modulus is in the range of 100.degree.-110.degree. C., (2) the above-mentioned storage modulus at 150.degree. C. is 1.times.10.sup.4 or less and (3) the peak temperature of the loss modulus is 125.degree. C. or more.
Due to control of the visco-modulus as described above, toner performance is improved to some extent. However, it is a current circumstance that a toner excellent in high speed and low temperature fixing performance, anti-hot offset performance, anti-smearing performance, and anti-coagulation performance has not been obtained.